Orthophorization after occlusion-induced exotropia

A 36-year-old male had been constantly wearing a patch to avoid diplopia since an operation on the right parietal area of the brain. Postsurgical visual field evaluation indicated a complete bilateral left hemianopia with macular splitting. The patient had a constant alternating comitant exotropia with no suppression. By terminating the patching, establishing the appropriate fixing eye, and applying relieving prisms, diplopia was removed. Once binocularity was thus established, it was found (over the course of 7 months) that binocular function was possible with diminishing amounts of prism power. During this 7-month period, measurements of the patient's heterophoria, motor fusion, and sensory fusion revealed that he adapted from his occlusion-induced exotropia toward an habitual heterophoria. Such vergence adaptation has been defined as orthophorization. The occurrence of vergence adaptation after sensory fusion indicates that sensory fusion plays an important role in the etiology of prism adaptation.